1. Field of the Invention
The present invention relates to thermal mass transfer donor elements and particularly to thermal mass transfer donor elements which provide a metallic appearing image upon thermal transfer.
2. Background of the Invention
Thermal mass transfer imaging processes are finding increasing application in the marketplace and provide environmentally sound, dry imaged processes. A thermal mass transfer donor sheet is placed in contact with a receptor sheet (which may be specifically designed for use in mass transfer or may be a conventional paper or film), the donor sheet is heated in an imagewise manner (usually from the backside) with localized heating effected by a thermal print head, irradiation through a mask or stencil, or coherent light imaged as with a laser or, light emitting diode, or solid state laser. The imagewise distribution of heat causes an imagewise transfer of material from a surface of the donor to the receptor which is in contact with that surface. The material which is transferred is usually a binder containing colorant (e.g., a dye, pigment, or both dye and pigment). The binder is a thermally softenable material which releases from a carrier layer on a carrier layer on the donor element and adheres and transfers to a receptor sheet.
Thermal mass transfer imaging, like most other forms of imaging, has traditionally used the primary additive and subtractive colors (and black) as the colorant in the donor transfer layers. In commercial situations it has become desirable to be able to provide additional colors beyond red, yellow, green, blue, cyan, and magenta (and black). Tailored colors, fluorescent colors, and metallic images are desirably available to the image maker.
Metal image forming impact printing elements have been disembeded with a vapor deposited metal film with a binder as a separate layer. U.S. Pat. No. 4,472,479 (Hayes et al.) describes an impact printing donor element which can provide a metallic appearing image which comprises a carrier layer and an impact transferable layer(s) containing metal particles or particles with metallic colors (e.g., mica flakes with coatings thereon). All working examples are of non-metal flakes with coatings thereon. A dye may also be present in the transferable layer(s) to improve the tone of the metal color.
A paper entitled "New Color Thermal Transfer Printing Media" presented to "The 5th International Congress on Advances in Non-Impact Printing Technologies" in San Diego, Calif., Nov. 12-17, 1989, described a thermal metallic transfer ribbon having an anchoring layer interposed between the vapor deposited metal and a release layer to secure the vapor deposited metal to the release layer.
U.S. Pat. No. 4,868,049 (Nelson) teaches a transfer sheet comprising, in successive layers, a carrier film, a metallic film, and an adhesive. Optionally, the transfer sheet further comprises, in successive layers, a release coat and a polymer coat interposed between the carrier film and the metallic film, and a primer coat interposed between the metallic film and adhesive. A preferred release coat is said to be made from an ethylene vinyl acetate copolymer.
U.S. Pat. No. 4,875,961 (Oike et al) discloses a heat-sensitive medium comprising a support, and a transfer layer comprising at least a non-flowable ink layer and an adhesive layer, said two layers being provided in that order from the support side. Optionally, a lubricant layer may be interposed between the ink layer and the support.
The metal-particulate containing mass transfer donor element such as that shown by Hayes et al. (U.S. Pat. No. 4,472,479) does not provide a high resolution, shiny metallic image. The films in which the metal layer is vapor deposited do not form high quality, high resolution imaging donors. To provide the most desirable thermal mass transfer metal appearing donor elements, it would be necessary to provide both a better reflecting (shinier) metal image and an image with greater resolution than that available from vapor deposited metallic donor layers.